This article describes the leading structural and superficial properties of zeolites which can be advantageously used as acid or bifunctional catalysts and as supports offering a considerable capacity for dispersing transition metal as well as interesting selective effects.The rather encouraging results obtained in heterogenizing various transition-metal complexes on org anic polymers or on silica have been used to measure the advances made in the field of incorporating them in zeolites. The scientific and pratical impor-tance of such an operation would be considerably enhanced if such complexes could be « encaged » in molecular-size cavities in zeolites or in recently-synthetized silicates whose crystallization is characterized by very slow kinetics.